Consistency Is Key

I've come to the realisation that in relationships, consistent behaviour helps stablise a couple.

Think of it like a stockmarket. I would argue that consistent quirks (sometimes a bad behaviour, maybe something that annoys one partner) would not break a couple down. Perhaps consistently bad behaviour will break up a couple, like some death by a thousand cuts. Everyone has their own quirks, and each couple will have their own rules and behaviours. However when one person strays from that expected response, it casts doubt on their other areas.

It is the "inconsistent quirk" that has the potential to threaten an otherwise stable relationship. The inconsistent quirk could be not standing up for your partner, or attempting to split a bill when usually we don't. That's the volatility that puts the relationship outside the normal bounds and makes people think more about whether this person is "really right".

Of course, all this does not change the fact that a bad behaviour is something that needs to be addressed, for a relationship to become better, not just stable. On that point, a unexpected surprise in good behaviour takes the relationship to the next level. And we all love surprises :)